Light sensitive apparatus



Dec. 18, 1934. H H (j,lip-.FCKEn-l.` Ef AL 1,985,086

LIGHT SENSITIVE' APPARATUS Filed Lmy 25, 195C Patented Dec. 1.8, 1934 LIGHT SENSITIVE APPARATUSV Heinrich Hermann Getcken and 4Hans Rudolf Richter, Leipzig, Germany, assignors to Radio Patents Corporation, New York, N. Y., a corf f poration of New York Application July A25, 1930, Serial No. 470,690 Y In GermanyV August 5, 1929 4 claims.` (c1. 25o-427.5)

In light sensitive tubes which are subjected'to intense illumination, the light sensitive layer easily becomes heated considerably, which leads to evaporation of the volatile cathode material and therefore to destruction of the light sensitive surface and to the formation of disadvantageous deposits.

One object of the present invention is to overcome Vthe aforementioned disadvantages'and to providea photo-electric tube which is selfregenerating by redepositing light sensitive sub- Stance which has become evaporized orV otherwise removed during operation, again on these parts carrying the light sensitive layer. 1

Another object of the invention consists in the provision of a photo-electric tube .which insures increased operating stability and life.

The invention will be described in greater detail in reference to the accompanying drawing in which Fig. 1` shows schematically a photo-electric tube of the usual construction, presented for the sake of better explanation of the invention;

Fig. 2 shows one embodiment of anovel construction of a photo-electric tube in accordance with the invention;`

Fig. 3 is another form of a new photo-electric tube construction according to the invention.

This invention relates to a new construction of light sensitive devices which has not these disadvantages. Photo-electric tubes are used, in which the photo-electric layer is precipitated on the inner tube wall in the usual manner, using a conducting base (e. g; asilver coating), but in which the base and the layer are kept so thin as to be to a considerable extent translucent. According to the invention, these tubes are so arranged that the incident light passes through the said thin layer and its base into the tube. Whereas photo-electric tubes, such as shown in an ordinary construction in Fig. 1 (tube Vessel 1, anode 2, thick photo-electric layer 3) are usually illuminated in the direction of the arrows 4, according to the invention the illumination is eiected in the direction of the arrows 5. It is thus achieved that a considerable fraction particularly of the infra-red and red parts of the radiation is reected by the tube, and the tube remains cool even under intense illumination. In spite of this, however, the photo-electric current with a suitable form of tube is not noticeably less or is even greater, than when the illumination is effected in the hitherto usual manner.

Very favourable results are obtained when platinum which has a very high reflecting power for infra-red, as against a comparatively low one for yellow, blue .and ultra-violet, is used as the conducting base for the light sensitive layer. In addition, platinum has all the other properties necessary for the base for the light sensitive layer in photo-electric tubes to a greater extent;

Through the arrangement according to the invention, tube forms are obtained which, besides the heat protection described, have very great advantages from a technical, as well as the economical standpoint. Firstly, the invention makes it possible, to produce tubes which make the best Ypossible use of the space, and-for a given sizehave the highest sensitivity, by the whole available useful inner side of the tube wall being covered with a light sensitive layer. Fig. 2 shows a tube of this kind in accordance with the invention with a spherical vessel 1.` The anode 2 also spherical if necessary, and the light sensitive layer 3 indicated by a thickening of the part of thewall concerned. As maybe seen, the tube is made quite symmetrical in all directions apart from the socket and consequently gives favourable optical and electrical results. The rays passing through the light sensitive layer and its base from anyr side rst produce their effecten passing through and then are distributed over the interor (as in the tube described in German Patent 312,250) by cross reflections from the remainder of the light sensitive surface, where they produce their effect in the usual manner. In order to prevent the rays from passing out of the tube again as far as possible, it is in many cases of advantage to make the light sensitive layer and its base so thin as to be translucent on the side at which the light enters, but more or less opaque at other places. It is also desirable to construct the anode in a known manner in the form of ya transparent body (net grid, spiral or also a glass body covered with a transparent metal layer or the like), also that during the cross reflections described there is no loss of light at the anode.

A substantial constructional advantage of a i tube according to the invention consists in this, that it is no longer necessary carefully to free a window from the light sensitive deposit. Further the base is more easily produced when it is not necessary to take account of the protection of a window. The base can thus be produced without special precautions by atomization or it can even be dispensed with if the necessary small amount of light sensitive material is applied by glass electrolysis in the tube vessel by which means a cohesive conducting layer can be In the tubes according to the invention ,the layers on the part at which the light enters need not be--as in the known so called thin metal` layers-completely clearand transparent, as a rule a translucency which is scarcely perceptible by reflected light is suicient. 'The actual light.

sensitive active layer can however be kept as thin as desired (if necessary even monatomic). If however the base layer is made very thin, it is often oi advantage, to lay at first a coarse-meshed net or grid of wires connected with theV conductor on the glass wall for obtaining a good contact with the conductors for producing this base layer. The conducting cohesiveness of the actual layer then only needs to be yassured'in small areas.

A particular advantage oi the invention consists in this, that it allows of the construction of extremely symmetrical forms of tubes. The tube illustrated in section in Fig. 3 is very favourably constructed in this respect in that the anode consists in a concentric inwardly projecting part 6 covered with a conducting layer in the tube vessel. The sensitivity of suchtubesis the same in all directions perpendicular to the longitudinal axis. As in a suitably constructed spherical tube, there is no possibility of the formation 'of wall charges so that freedom from lag is assured, and the law of proportionality between the photoelectric current and the illumination is vconipletely satisfied. Finally tubes of this kindon account oi the favourable field-distribution produce a very high photo-electric current even without any applied voltage.

A further important advantage of photo-electric tubes according to the invention in which the translucent light sensitive layer is applied to the entire useful portion of the inside wall of the tube maintained at the lowest temperature by direct contact with the surrounding air (surface 3), consists in a kind of self-regenerating effect in that light sensitive material which becomes evaporized during operation, is always dew Dosited .again at the cathode surface constituting'the coolest part of the tube. Thus :the life of the tube is increased.

What I claim is:-

1. A photo-electric tube, comprising a sealed tubular vessel having a reentrant tubular portion concentric with said vessel, and a translucent light sensitive `cathode iilm, covering the entire useful inside Wall of said tube, excepting said reentrant portion; and an anode-electrode within said vessel.

v2. A photo-electric tube comprising a sealed transparent vessel having a translucent base consisting of platinum; a translucent light sensitive layer covering said base portions of the inside wall of said vessel maintained at a lower temperature by Adirect Contact with the surrounding air than the remaining portion of said vessel;

land an anode lelectrode within said vessel.

3. A photo-electric tube comprising a sealedl transparent vessel having an outer wall and a reentrant inner wall; a translucent light sensitive cathode layer covering substantially the entire inner portions of said outer wall and an anode electrode covering substantially the entire surface of said inner wall, whereby the surrounding heat generated by the operation of saidvessel is 'absorbed by said anode to maintain the anode .at a higher temperature than the cathode electrode. 4. A photo-electric tube lcomprising a sealed transparent vessel, a translucent metallic base coated with a translucent light Lsensitive layer covering a portion 'of the inside wall of said vessel. a large anode surface within said `vessel disposed opposite and substantially equi-.distant from :said .layer whereby heat produced during the operation of said tube is absorbed by said anode to maintain Asame at a higher temperature than said cathode.

HEINRICH HERMANN GEFFCKEN.

HANS RUDOLF RICHTER. 

